title: A comparison of ether- and alkyl-derivatized imidazolium-based room-temperature ionic liquids: a molecular dynamics simulation study.
abstract: Molecular dynamics simulations of ether-derivatized imidazolium-based room-temperature ionic liquids (EDI-RTILs), [C(5)O(2)mim][TFSI] and [C(5)O(2)mim][BF(4)], have been performed and compared with simulations of alkyl-derivatized analogues (ADI-RTILs). Simulations yield RTIL densities, self-diffusion coefficients and viscosity in excellent agreement with experimental data. Simulations reveal that structure in the EDI-RTILs, quantified by the extent of nanoscale segregation of tails as well as cation-ion and cation-cation correlations, is reduced compared to that observed in the ADI-RTILs. Significant correlation between ether tail oxygen atoms and imidazolium ring hydrogen atoms was observed in the EDI-RTILs. This correlation is primarily intramolecular in origin but has a significant intermolecular component. Competition of ether oxygen atoms with oxygen atoms of TFSI(-) or fluorine atoms of BF(4)(-) for coordination of the ring hydrogen atoms was found to reduce the extent of cation-anion correlation in the EDI-RTILs compared to the ADI-RTILs. The reduction in intermolecular correlation, particularly tail-tail segregation, as well as weakening of cation-anion specific interactions due to the ether tail, may account for the faster dynamics observed in the EDI-RTILs compared to ADI-RTILs.
authors.affiliation: Department of Materials Science and Engineering, University of Utah, 122 S. Central Campus Drive, Salt Lake City, UT 84112, USA.
authors.forename: Grant D
authors.initials: GD
authors.lastname: Smith
authors.forename: Oleg
authors.initials: O
authors.lastname: Borodin
authors.forename: Liyong
authors.initials: L
authors.lastname: Li
authors.forename: Hojin
authors.initials: H
authors.lastname: Kim
authors.forename: Qin
authors.initials: Q
authors.lastname: Liu
authors.forename: Jason E
authors.initials: JE
authors.lastname: Bara
authors.forename: Douglas L
authors.initials: DL
authors.lastname: Gin
authors.forename: Richard
authors.initials: R
authors.lastname: Nobel
mesh_terms: D000473:Alkanes / Q000737:chemistry*; D003198:Computer Simulation; D004058:Diffusion; D004987:Ethers / Q000737:chemistry*; D007093:Imidazoles / Q000737:chemistry*; D052578:Ionic Liquids / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D010100:Oxygen / Q000737:chemistry; D011789:Quantum Theory; D013816:Thermodynamics; D014783:Viscosity
chemical_list: D000473:Alkanes; D004987:Ethers; D007093:Imidazoles; D052578:Ionic Liquids; D010100:Oxygen